Reticle Suction Frame for Photolithography Flatness
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Solution Overview
Problem
Large reticles in photolithography equipment experience significant gravity-induced warpage, affecting exposure accuracy and image quality, with existing correction methods increasing structural complexity or impacting illumination system performance.
Innovation Solution
An apparatus comprising a sucker mounting frame with spaced suckers and a pneumatic control system that applies adjustable suction forces to counterbalance reticle gravity, ensuring non-contact retention and independent operation from the photolithography tool components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a glass plate is mounted between the reticle and illumination system to apply upward force, then reticle gravity-induced bending is offset, but the glass plate blocks light beams and affects illumination system performance
Solution Approach 1:
The invention extracts the light-blocking glass plate from the optical path by relocating the suction application point to the reticle back surface. The suction holes are positioned outside the light beam path, allowing light to pass through the reticle front surface without obstruction while still applying corrective suction force through the reticle substrate to maintain flatness.
Solution Approach 2:
The reticle substrate itself serves as an intermediary medium to transmit the suction force from the rear surface to the front surface where the light passes through. The suction applied at the back surface is transmitted through the reticle material to correct the bending without requiring any physical presence in the light path.
2Shape
If multiple components (reticle, glass plate, pneumatic device) are arranged on the same frame, then reticle warpage correction is achieved, but vibration and weight load increase
Solution Approach 1:
The invention extracts and removes the heavy glass plate from the system entirely, replacing it with a lightweight pneumatic suction system applied directly to the reticle back surface. This eliminates the additional weight and vibration sources associated with the glass plate while maintaining the warpage correction function.
Solution Approach 2:
The suction force is applied locally and selectively at specific positions on the reticle back surface through strategically positioned suction holes. This localized application allows precise control of the corrective force where needed, rather than requiring a heavy universal support structure.
3Reliability
If suction holes are positioned within exposure fields, then reticle retention is achieved, but exposure efficiency is reduced due to light beam blocking
Solution Approach 1:
The invention inverts the conventional approach by applying suction from the reticle back surface rather than the front surface. This reversal allows the suction holes to be positioned outside the exposure fields on the rear surface, eliminating light blockage while maintaining secure reticle retention through the substrate.
Solution Approach 2:
The suction holes are extracted from the light path area and relocated to the reticle back surface. This spatial separation ensures that the retention mechanism (suction holes) does not interfere with the exposure process, as they are positioned in a region where light beams do not pass.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively corrects reticle shape without blocking exposure fields, reduces weight load, and prevents gravitational deformation, enhancing exposure efficiency and image quality while minimizing vibration and thermal deformation.
Implementation Method 1
The pneumatic control system is configured to control the plurality of suckers to retain the reticle by suction or to release the reticle
Implementation Method 2
its downward bending due to gravity is inevitable, which can be as great as up to over 40 μm
Data Source
AI summary
An apparatus for correcting the shape of a reticle, including: suckers; a sucker mounting frame; and a pneumatic control system, wherein the sucker mounting frame is disposed above a reticle stage, the suckers are mounted on a bottom of the sucker mounting frame in a manner of being spaced apart from one another; and the pneumatic control system is configured to control the suckers to retain the reticle by suction or to release the reticle. The suckers are so arranged that they do not block trapezoidal exposure fields of view on the reticle, thereby allowing a light beam to be fully (100%) incident on the reticle, which results in improved exposure efficiency. The apparatus is mounted separately from a photolithography tool by which it is employed, enabling a lower weight load on the reticle. Additionally, the apparatus is not in contact with any component disposed in the photolithography tool and will not introduce additional external vibration to the tool.